1. Field of the Invention
This invention relates generally to a method and apparatus for handling optical waveguide substrates and, more particularly, to a fixture and a method for handling optical fibers and similar waveguides for processing.
2. Description of the Prior Art
Optical waveguides, including fiber and fiber-like substrates such as optical fibers, are known. It is also known to change the useful properties or characteristics of selected areas of an optical waveguide by first exposing the optical core and/or the optically transmissive cladding to permit processing of the core and/or the cladding. For example, U.S. Pat. No. 4,182,664 to Maklad et al., discloses processing by which optical fibers become relatively stable to nuclear radiation loss by pre-irradiating the fibers.
U.S. Pat. No. 4,793,680 to Byron discloses the formation of a grating by directing a pulsed high-power laser beam on or near an exposed end of an optical waveguide to create rippled discontinuities on the waveguide. Other processes form optical patterns of varied optical densities or refractive indexes. U.S. Pat. No. 4,403,031 to Borrelli et al. discloses a process for forming optical patterns of varied optical densities or refractive indexes by exposing porous glass impregnated with a photolyzable organometallic compound to photolyzing light.
Other processing forms Bragg gratings in the core and/or cladding layers of optical fibers. These fibers are particularly adapted for use in strain sensing, stress sensing, temperature sensing, pressure sensing, vibration sensing, and other sensors. In one such method, apparatus directs coherent green light (approximately 488 nm wavelength) into both ends of a germania doped optical fiber. The resulting interference pattern photobleaches the core of the fiber and thereby creates a grating.
U.S. Pat. Nos. 5,066,133 to Brienza, 5,061,032 to Meltz et al., 5,042,897 to Meltz et al., 4,793,930 to Blyler, Jr. et al., and 4,725,110 to Glenn et al. disclose apparatus for focusing and directing split beams of coherent light in the ultraviolet region (approximately 244 nm wavelength) onto a specific region of a germania doped optical fiber. An analogous process disclosed in U.S. Pat. No. 5,104,209 to Hill et al. forms Bragg gratings in europium and alumina doped fibers.
In general, such processing of optical waveguides comprises successive steps. When more than one region or segment requires processing, each region is processed successively. Sequential processing frequently introduces other perturbations including, for example, dimensional variations, planar variations, and consistency variations.
The consecutive nature of these operations also increases the time needed for the processing of individual fibers. Repeated handling of the fiber increases the potential of breakage in the processed region thereby limiting the amount of processing or requiring extra care in the handling of the fiber.
As a final step in processing, it is often desirable to apply or reapply a protective coating over the processed waveguide. Various methods which are known or suggested for applying such protective coatings include extrusion, overmolding, and vapor-phase deposition processes. Extrusion processes generally involve drawing the fiber individually through the coating material and risk fiber breakage. Overmolding processes involve disposing a pre-formed, over-sized covering or tube over the fiber and filling the tube with a molding material which bonds the tube to the fiber. The overmolding process frequently introduces undesirable mechanical properties and also increases the potential for fiber breakage. Vapor-phase deposition techniques typically deposit very thin coatings (i.e., in the micron range) of materials generally not useful for protective coatings for such fibers.
U.S. Pat. No. 4,040,691 to David et al. discloses a fixture in the form of a waveguide holder-humidifier comprising a rectangular container and a hinged top. Holes in two sides of the container enable a liquid sample to pass through the container. U.S. Pat. No. 4,793,681 to Barlow et al. discloses a relatively complicated splice cradle for holding fiber optic splice segments in place. U.S. Pat. No. 4,721,586 to Kakii et al. discloses a mold which mounts optical fibers of a cable as part of a method for forming cable plugs. A resin is introduced into the mold to solidify about multiple optical fibers of a single cable which are then cut apart to form two plugs. U.S. Pat. No. 4,750,804 to Osaka et al. discloses a jig securing single or plural optical fiber cores for fusion welding with other similarly secured cores.
The foregoing references fail to provide a fixture for holding optical waveguides for processing to alter the properties of optical waveguides. They fail to provide a fixture that is relatively simple to use and that reduces the direct handling of optical waveguides during processing and that enables concurrent processing by a variety of techniques of waveguides secured in the fixture. Additionally, the prior art fails to suggest a fixture that is simple to use and that facilitates the formation of a protective coating about exposed portions of the optical waveguide.